Peanut butter is a spreadable food made from crushed peanuts, often with salt and sugar, and is popular among English-speaking countries such as the UK, United States, and Australia, among others. Peanut butter was incorporated into the storyline of Lost several times.

Charlie wanted Claire to move to the Caves. She refused unless he could find her a jar of peanut butter. He asked Hurley, who had none. He ultimately convinced her to move by offering an empty jar of pretend peanut butter. ("Confidence Man") When the hatch was opened and food divided up, Hurley gave Charlie a jar and Charlie finally gave Claire real peanut butter. ("Everybody Hates Hugo")

Hurley took a jar of peanut butter with him when he went off to be alone. It fell from his backpack and broke open, and he began eating it with a leaf. Dave appeared right after and said irritably that Hurley got some on his shoe. Also, Hurley had some peanut butter in his secret stash of food that he had revealed to Libby in the same episode. ("Dave")

The official jigsaw puzzles contains several secret messages, one of which reads "WHAT GOOD IS PEANUT BUTTER AND CEREAL WITHOUT MILK".